Accelerated replicative senescence of the peripheral immune system induced by HIV infection

OBJECTIVES: HIV induces rapid turnover of T lymphocytes but whether this leads to replicative senescence of CD4+ and CD8+ cells and contributes to AIDS symptoms is unclear. The aim of this study was to address this question by analyzing telomere length in blood cell populations as a measure of replicative history in a significant number of patients infected with HIV. DESIGN: Total peripheral blood mononuclear cells (PBMCs), CD4+ or CD8+ cells were isolated from blood collected from a total of 73 HIV patients and 27 controls. Samples were isolated to measure telomere length, telomerase activity and proliferative ability, and analyses were carried out in a blind experimental protocol. METHODS: PBMCs isolated on Ficoll-Hypaque gradients were washed and prepared for additional fractionation into CD4+ and CD8+ cells using antibody-bound magnetic beads. Total PBMCs, CD4+ and CD8+ cells were used for cell cycle analysis, for telomerase activity assays and were measured for telomere length using the terminal restriction fragment assay. RESULTS: Telomere analyses in this study show a clear (P < 0.0001) inverse relationship between telomere length and progression of immunosuppression, with HIV infection resulting in a five-fold or greater acceleration of aging of the circulating PBMC component of the immune system. Patients who are 37 years old showed telomere lengths similar to uninfected 75-year-olds. Telomere loss correlated well with progression of AIDS and with reduced proliferative ability of patient PBMCs but was unrelated to telomerase activity. Mean telomere length was shorter in both CD4+ and CD8+ cells, with three-fold higher rates of telomere loss for CD8+ lymphocytes. CONCLUSIONS: These data provide strong support for the occurrence of accelerated replicative aging of the peripheral immune system, possibly resulting in a loss of T cells leading to AIDS symptoms.     

The flow cytometric analysis of telomere length in antigen-specific CD8+ T cells during acute Epstein-Barr virus infection

Acute infectious mononucleosis (AIM) induced by Epstein-Barr virus (EBV) infection is characterized by extensive expansion of antigen-specific CD8+ T cells. One potential consequence of this considerable proliferative activity is telomere shortening, which predisposes the EBV-specific cells to replicative senescence. To investigate this, a method was developed that enables the simultaneous identification of EBV specificity of the CD8+ T cells, using major histocompatibility complex (MHC) class I/peptide complexes, together with telomere length, which is determined by fluorescence in situ hybridization. Despite the considerable expansion, CD8+ EBV-specific T cells in patients with AIM maintain their telomere length relative to CD8+ T cells in normal individuals and relative to CD4+ T cells within the patients themselves and this is associated with the induction of the enzyme telomerase. In 4 patients who were studied up to 12 months after resolution of AIM, telomere lengths of EBV-specific CD8+ T cells were unchanged in 3 but shortened in one individual, who was studied only 5 months after initial onset of infection. Substantial telomere shortening in EBV-specific CD8+ T cells was observed in 3 patients who were studied between 15 months and 14 years after recovery from AIM. Thus, although telomerase activation may preserve the replicative potential of EBV-specific cells in AIM and after initial stages of disease resolution, the capacity of these cells to up-regulate this enzyme after restimulation by the persisting virus may dictate the extent of telomere maintenance in the memory CD8+ T-cell pool over time.     

Regulatory T Cell Subtypes and TGF-β1 Gene Expression in Chronic Allograft Dysfunction

Background: Regulatory T cells have been suggested to have a protective role against acute rejection in allograft recipients. However, there is little information available about their contribution to chronic rejection process. The role of transforming growth factor-beta 1 (TGF- β1) as a profibrogenic and/or immunoregulatory cytokine in renal allografts is also controversial. Objectives: To evaluate the frequency of CD4+CD25+CD127- and CD3+CD8+CD28- regulatory T cells in chronic allograft dysfunction (CAD) and to investigate the expression of TGF- β1 in renal allografts. Methods: Thirty biopsy-proven CAD patients were pair-matched with 30 stable graft function patients and a third group of healthy volunteers. Flowcytometry was performed on PBMCs to determine the frequency of CD3+CD8+CD28- and CD4+CD25+CD127- regulatory T cells in lymphocyt population. TGF- β1 gene expression was assessed by Real Time PCR. Results: The percentage of CD3+CD8+CD28- Tregs among renal allograft recipients was higher than healthy controls (p<0.001) since stable graft patients showed the most rates. The frequency of CD4+CD25+CD127- Tregs was lower in CAD patients than stable recipients (p=0.024) and healthy group (p=0.015). TGF- β1 gene expression was greater in CAD patients compared to healthy group (p=0.03) but there was no significant difference between gene expression of stable graft patients and healthy volunteers. Conclusion: The negative association between the frequency of regulatory T cell subtypes and chronic allograft dysfunction proposes these cells as probable candidates for promoting allograft survival. Moreover, despite the immunoregulatory capacity of TGF- β1, it is likely to be implicated in chronic damages of allograft tissue.     

Immunoexpression of perforin and granzyme B on infiltrating lymphocytes in human renal acute allograft rejection

Graft destruction can be effected by direct cell-to-cell contact between activated effector T cell and a target graft resulting in delivery of cytotoxic molecules. Perforin and granzyme B can be used as activation markers for cytotoxic cells in allograft tissue. The aim of the study was to determine the immunoexpression of perforin and granzyme B by immune cells infiltrating renal tissue during acute allograft rejection and to evaluate any correlation between the phenotype of infiltrating lymphocytes and cells expressing cytotoxic granules as well as the severity of graft damage as defined by Banff 97 criteria. Immunoperoxidase staining was carried out using monoclonal antibodies anti-perforin, -granzyme B, -CD3 and -CD8 on renal allograft biopsy specimens from twenty one patients with acute renal transplant rejection: Banff 97 IA (n = 11) and Banff 97 IB (n = 10). As a control 11 biopsy specimens of renal transplant patient without any signs of rejection were used. All allograft biopsy specimens with acute renal transplant rejection contained a high number of CD3+ T cells (Banff IA: 437.4 +/- 154.4 and Banff IB: 825 +/- 339.9 vs 123.4 +/- 52.5 in controls) and CD8+ T lymphocytes (Banff 97 IA: 177.6 +/- 89.2 and Banff IB: 293.2 +/- 112.4 vs 64.2 +/- 37.1 in controls). Immunostaining for granzyme B and perforin was negative in controls. The immunopositivity for perforin was similar in Banff IA and Banff IB acute allograft rejection (1.5 +/- 0.6 vs 1.8 +/- 0.8, respectively). Granzyme B+ cell count was significantly higher in severe rejection group Banff IB (128.3 +/- 74.3) than in Banff IA group (48.2 +/- 18.3). Moreover, in acute allograft rejection Banff IB the number of granzyme B+ cells and perforin+ cells was correlated with the number of CD8+ T cells. In conclusion, our results suggest that in acute tubulointerstitial allograft rejection activated cytotoxic T lymphocytes play a major role. The strong immunopositivity for granzyme B on infiltrating cells in renal transplant tissue is suggested as a marker of severity of graft damage.     

T-cell telomere length maintained in HIV-infected long-term survivors

Background and methods We have used the erosion of telomeric DNA as a measure of cellular division to study the replicative history of isolated T-lymphocyte subpopulations from a group of HIV-infected long-term survivors and age-matched healthy controls.
Results In keeping with previous studies, we found that CD45RO⁺ (memory) T-cells showed greater telomere erosion than CD45RA⁺ (naive) T-cells. We did not, however, find any significant differences in the telomere lengths of isolated CD4⁺, CD8⁺, CD45RA⁺ or CD45RO⁺ T-cells between HIV-infected long-term survivors and age-matched controls. Further, we found no evidence of telomerase activation in
T-cells from the HIV-infected groups to account for the lack of telomere erosion.
Conclusions Our data show no evidence, through telomere shortening, of clonal exhaustion or replicative senescence due to an increased rate of immune cell turnover in HIV-infected long-term survivors.     

Integration of apoptosis and telomere erosion in virus-specific CD8+ T cells from blood and tonsils during primary infection

Human-virus-specific CD8+ T cells that are found during primary infection have been studied almost exclusively in the peripheral blood, and it is unclear whether these cells are regulated in the same way as those in secondary lymphoid tissue. We investigated, therefore, the control of apoptosis and telomere erosion of Epstein-Barr virus (EBV)-specific CD8+ T cells found in the blood and tonsils of the same patients during acute infectious mononucleosis (AIM). Although the clonal composition of CD8+ T cells as determined by heteroduplex analysis was similar in both compartments, there was greater CD28 expression in the tonsil population, indicating that they were less differentiated. EBV-specific CD8+ T cells in both tissue types were extremely susceptible to apoptosis related to low Bcl-2 expression and were dependent on exogenous cytokines such as interleukin-2 (IL-2), IL-15, and interferon-alpha/beta (IFN-alpha/beta) for survival. In both compartments, however, these cells maintained their telomere lengths through telomerase induction. Thus, apoptosis-prone EBV-specific CD8+ T cells found during acute infection have to be rescued from death to persist as a memory population. However, signals that induce telomerase ensure that the rescued cells retain their replicative capacity. Significantly, these processes operate identically in cells found in blood and secondary lymphoid tissue.     

Indications for a disturbed peripheral T-cell homeostasis in juvenile idiopathic arthritis (JIA): absent expansion of CD28 T-cells and no decrease of naive T-cells in cytomegalovirus-positive patients with JIA

OBJECTIVE: To investigate the influence of latent cytomegalovirus (CMV) and Epstein-Barr virus (EBV) infections on CD28-expressing T-cell subpopulations and replicative senescence of naive T-cells as a marker for aging of the immune system in children with juvenile ideopathic arthritis (JIA). METHODS: T-cell subpopulations were analyzed from 24 patients with JIA and 61 healthy age-matched controls by fluorescence activated cell sorting. Relative telomere length (RTL) in CD4+CD28+CD45RA+ (naive) T-cells was measured by quantitative polymerase chain reaction. RESULTS: Although confirming known data of expansions of CD28- T-cells and tendency of decreasing naive T-cells in CMV-seropositive healthy individuals, our findings did not show a marked influence of latent EBV or CMV infection on CD28-expressing T-cells in patients with JIA. In contrast, CMV was an independent factor for loss of CD28, regardless of age, in healthy controls. Irrespective of serology results for CMV or EBV, patients with JIA showed signficantly decreased RTL compared to age-matched controls. Regression lines for RTL and age revealed decreased RTL with advancing age in CMV-positive and EBV-positive subjects. The evidence that findings for CMV-positive JIA patients did not resemble the findings of healthy CMV-positive controls, namely expansion of CD28- T-cells and decrease of naive T-cells, may support the theory of a disturbed peripheral T-cell homeostasis in JIA. CONCLUSION: Diminished mechanisms of T-cell homeostasis and premature aging of the immune system may play a role in the pathogenesis of JIA.     

Telomerase induction in T cells: A cure for aging and disease?

Cells of the immune system are unique among normal somatic cells in that they have the capacity to upregulate the telomere-extending enzyme, telomerase, albeit in a precisely controlled fashion. Kinetic analysis of telomerase activity in long-term T cell cultures has documented that the high level of telomerase induced in concert with activation reaches a peak at 3-5 days, then declines by 3 weeks. The process is recapitulated during secondary antigenic stimulation, but by the third, and all subsequent stimulations in vitro, CD8 T cells are unable to upregulate telomerase. Cell division in the absence of telomerase activity results in progressive telomere shortening, and ultimately, the DNA damage/cell cycle arrest that is signaled by critically short telomeres. Cultures of senescent CD8 T cells show altered cytokine patterns, resistance to apoptosis, and absence of expression of the CD28 costimulatory receptor. CD8 T cells with these and other features of replicative senescence accumulate progressively with age, and at an accelerated rate, during chronic infection with HIV-1. Clinical studies have shown that high proportions of CD8 T cells with the senescent phenotype correlate with several deleterious physiologic outcomes, including poor vaccine responses, bone loss, and increased proinflammatory cytokines. CD8(+)CD28(-) T cells have also been shown to exert suppressive activity on other immune cells. Based on the central role of telomere shortening in the replicative senescence program, we are developing several telomerase-based approaches as potential immunoenhancing treatments for aging and HIV disease. Gene therapy of HIV-specific CD8 T cells with the telomerase catalytic component (hTERT) results in enhanced proliferative capacity, increased anti-viral functions, and a delay in the loss of CD28 expression, with no changes in karyotype or growth kinetics. These proof-of-principle studies have led to screening for pharmacological approaches that might mimic the gene therapy effects, in a more clinically suitable formulation.     

In vitro senescence of immune cells

Immune cells are eminently suitable model systems in which to address the possible role of replicative senescence during in vivo aging. Since there are more than 10⁸ unique antigen specificities present within the total T lymphocyte population of each individual, the immune response to any single antigen requires massive clonal expansion of the small proportion of T cells whose receptors recognize that antigen. The Hayflick Limit may, therefore, constitute a barrier to effective immune function, at least for those T cells that encounter their specific antigen more than once over the life course. Application of the fibroblast replicative senescence model to the so-called cytotoxic or CD8 T cell, the class of T cells that controls viral infection and cancer, has revealed certain features in common with other cell types as well as several characteristics that are unique to T cells. One senescence-associated change that is T cell-specific is the complete loss of expression of the activation signaling surface molecule, CD28, an alteration that enabled the documentation of high proportions of senescent T cells in vivo. The T cell model has also provided the unique opportunity to analyze telomere dynamics in a cell type that has the ability to upregulate telomerase yet nevertheless undergoes senescence. The intimate involvement of the immune system in the control of pathogens and cancer as well as in modulation of bone homeostasis suggests that more extensive analysis of the full range of characteristics of senescent T cells may help elucidate a broad spectrum of age-associated physiological changes.     

Correlation of CD95 and soluble CD95 expression with acute rejection status of liver transplantation

AIM: To analyze the expression levels of soluble form of CD95, CD95 ligand (sCD95 and SCD95L, respectively) in plasma and CD95 expression on CD3+cells in liver-transplanted recipients with acute rejection (AR). METHODS: Peripheral blood mohonuclear cells (PBMCs) were isolated from 30 clinically liver transplanted recipients. CD95 expression on CD3+ cells was quantitatively measured by two-color fluorescence activated cell sorter (FACS) analysis. Lymphocyte surface phenotypes of CD4, CD8, CD16 and CD56 were determined by flow cytometry. Plasma levels of sCD95 and SCD95L were detected by Enzyme Linked-Immuno-Sorbent Assay (ELISA). The results were compared with that from normal healthy volunteers (n=15 individuals). RESULTS: FACS analysis showed that CD95 expression on CD3+ T cells was significantly increased in liver transplanted recipients with AR compared to that in stable recipients without rejection and infection or healthy individuals who did not undergo transplantation (18 676.93±11 588.34/molecule, 6 848.20±1 712.96/molecule, 6 418.01±2 001.95/molecule, respectively, P<0.01). Whereas no significant difference was seen between liver-transplanted stable recipients and healthy individuals. Furthermore, no significant differences were detected between each group with CD4/CD8 ratio or the percentage of CD16+56+cells. Plasma levels of sCD95 were significantly higher in transplanted recipients with AR compared to that in stable recipients or healthy individuals (391.88±196.00, 201.37±30.30, 148.83±58.25 pg/mL, respectively, P<0.01). In contrast, the plasma levels of sCD95L in liver-transplanted recipients were not significantly different from that in healthy individuals. CONCLUSION: The present results indicate that the increased CD95 expression on CD3+cells and the increased levels of sCD95 in plasma may modify the immunological situation of the recipients after transplantation or represent the ongoing graft rejection.     

Mucosal FOXP3+ regulatory T cells are numerically deficient in acute and chronic GvHD

CD4+CD25+ regulatory T cells (Tregs) control immune responses to self- and foreign antigens and play a pivotal role in autoimmune diseases, infectious and noninfectious inflammation, and graft rejection. Since recent experimental studies have indicated that Tregs were able to ameliorate graft-versus-host disease (GvHD), we analyzed the number of infiltrating Tregs in the intestinal mucosa as one site of GvH reactivity using immunoenzymatic labeling to enumerate FOXP3+ T cells in 95 intestinal biopsies from 49 allografted patients in comparison with healthy controls and patients with infectious inflammation. While patients with cytomegalovirus (CMV)-colitis or diverticulitis showed a concomitant increase of CD8+ effectors and Tregs, acute and chronic GvHD were characterized by the complete lack of a counter-regulation indicated by a FOXP3+/CD8+ T-cell ratio identical to healthy controls. In contrast, specimens without histologic signs of GvHD demonstrated increased numbers of FOXP3+ per CD8+ T cells, indicating that the potential for Treg expansion is principally maintained in allografted patients. Our findings provide evidence that GvHD is associated with an insufficient up-regulation of Tregs in intestinal GvHD lesions. The determination of FOXP3+/CD8+ ratio can be a helpful tool to discriminate GvHD from infectious inflammation after allogeneic stem cell transplantation.     

强直性脊柱炎患者外周血CD8+CD28-T细胞的表达及意义

目的 探讨外周血CD8+CD28- T细胞在强直性脊柱炎(AS)发病中的作用.方法 应用流式细胞术检测50例AS患者和21名正常人外周血CD3+CD8+ T细胞表面CD28分子的表达,同时用免疫散射比浊法检测相应血清中的C反应蛋白(CRP).结果 AS患者外周血中的CD8+CD28- T细胞的表达明显高于正常人[(18±6)%对(14±5)%,P=0.020],患者外周血CD3+、CD8+CD28+ T细胞的表达明显低于正常人[(65±9)%对(69±8)%,P=0.039];[(15±5)%对(18±4)%,P=0.038],CD8+ T细胞的表达与正常人相比差异无统计学意义(P＞0.05).结论 AS患者外周血中的CD8+CD28- T细胞的表达增加,可能参与了AS的疾病过程.     

Different rates of telomere shortening and telomerase activity reduction in CD8 T and CD16 NK lymphocytes with ageing

Telomeres are specialised structures located at the end of eukaryotic chromosomes, that get short during progressive cell divisions. Therefore, telomere may be an indicator of the mitotic history of a cell and it is also a determining factor for the residual cell life span. One mechanism, compensating for the telomere erosion, involves the induction of telomerase, a ribonucleoprotein-enzyme able to synthesize telomeric DNA repeats. In this study, old subjects of two consecutive decades were compared with a group of young controls to investigate whether ageing-related modifications differently affects telomere length and telomerase activity of human peripheral blood CD8 T and CD16 NK lymphocytes. Telomeres in individual cells were measured by flow-FISH and telomerase activity was determined using the TeloTAGGG telomerase PCR ELISA(PLUS) kit. Both CD8 T and NK lymphocytes showed an age-associated loss of telomeres at rates that were different between the subsets together with an age-associated reduction of telomerase activity that was progressive in CD8 and late in NK lymphocytes. We can assume that preserved innate immune response in the elderly is due to the negligible telomere shortening and the maintained telomerase expression that could allow NK cells of octogenarians to delay replicative senescence.     

Resistance to apoptosis in human CD8+ T cells that reach replicative senescence after multiple rounds of antigen-specific proliferation.

We have established an in vitro culture model of cellular aging in which antigen-specific T cells are stimulated repeatedly to divide until they reach the irreversible state of growth arrest known as "replicative senescence." T lymphocytes that reach replicative senescence in culture show complete loss of CD28 expression, shortened telomeres, undetectable telomerase, and reduced ability to produce heat shock proteins. We now document that in response to treatment with apoptotic stimuli, senescent CD8+ T-cell cultures show reduced apoptosis and diminished caspase 3 activity compared with quiescent early passage cultures from the same donor. Our results suggest that the progressive accumulation of T cells showing many of the hallmarks of replicative senescence during aging, chronic infection, and autoimmune disease may, in part, reflect the diminished capacity of such cells to undergo normal programmed cell death.     

Intraindividual variability and the effect of acute illness on immune senescence markers

OBJECTIVES: To determine the intraindividual variability and effect of acute illness on two markers of immune senescence. DESIGN: Cohort study with repeated measures. SETTING: Clinical research center and emergency department at two academic medical centers. PARTICIPANTS: Seventy-three subjects aged 65 and older enrolled in three groups: chronic underlying conditions but no acute illness, acutely ill with infection (community-acquired pneumonia), and acutely ill without infection. MEASUREMENTS: CD16 density on polymorphonuclear neutrophils (PMNs) and the proportion of CD8+ T cells that express CD28 determined twice in the nonacutely ill group and three times (Days 0, 30, and 60) in the acute illness groups. RESULTS: In the nonacutely ill group, PMN CD16 density demonstrated wide intraindividual variation, but there was a strong correlation for repeated measures of the percentage of CD8+ T cells expressing CD28 (correlation coefficient (r)=0.77, P<.001). Acute illness markedly affected both measures, regardless of whether the illness was due to infection; there was no correlation between measures obtained on Day 0 versus Day 30 for either immune marker. In contrast, a strong correlation existed between Day 30 and Day 60 values, particularly for CD8+/CD28+ percentage (r=0.58-0.86; P=.006 to <.001). CONCLUSION: The percentage of CD8+ T cells that express CD28 is a highly reproducible marker of immune senescence. Although acute illness affects this marker, 30 to 60 days of convalescence appears adequate for it to return to baseline.     

老年慢性阻塞性肺疾病患者外周血T细胞表达趋化因子受体3的研究

目的 探讨趋化因子受体3(CXCR3)在老年慢性阻塞性肺疾病(COPD)发病中的作用.方法 研究对象均为65岁以上的老年人,分为COPD急性加重期组(20例)、COPD稳定期组(17例)及对照组(14例),分离外周血单个核细胞,流式细胞仪检测CD4+和CD8+T细胞分别占总T细胞的百分比,CD4+CXCR3+T细胞占总CD4+T细胞的百分比,CD8+CXCR3+T细胞占总CD8+T细胞的百分比,以及CD4+CXCR3+和CD8+CXCR3+T细胞上CXCR3的平均荧光强度(MFI).结果 ①三组间及COPD急性加重期组治疗前后CD4+、CD8+T细胞分别占总T细胞的百分比,差异无统计学意义.②CD8+CXCR3+T细胞占总CD8+T细胞的百分比及CD4+CXCR3+T细胞占总CD4+T细胞百分比:COPD急性加重期组较COPD稳定组及对照组明显降低,COPD稳定组较对照组明显升高,差异有统计学意义,P＜0.05.CD4+CXCR3+和CD8+CXCR3+T细胞上CXCR3的MFI三组间差异无统计学意义.③COPD急性加重期组经治疗后CD8+CXCR3+T细胞占总CD8+T细胞的百分比及CD4+CXCR3+T细胞占总CD4+T细胞百分比,CD4+CXCR3+和CD8+CXCR3+T细胞上CXCR3的MFI,均明显降低,差异有统计学意义,P＜0.05.结论 COPD稳定期T细胞上CXCR3的过度表达在COPD慢性炎症过程中起作用.     

Elevated Th17 cells are accompanied by FoxP3+ Treg cells decrease in patients with lupus nephritis

To investigate the variations of T-helper 17 (Th17) and regulatory T (Treg) cells in patients with lupus nephritis (LN), a total of 60 systemic lupus erythematosus patients and 28 healthy controls (HCs) were enrolled. The frequency of Th17 cells and Treg cells in peripheral blood mononuclear cells (PBMCs) was evaluated by flow cytometric analysis. The serum concentrations of interleukin-17 (IL-17) and transforming growth factor-beta 1 (TGF-β1) were measured by enzyme-linked immunosorbent assay (ELISA). The results demonstrated in LN patients a significant decrease in the frequency of CD4+CD25^high and CD4+CD25+FoxP3+ T cells and a significant increase in the frequency of Th17 cells in peripheral blood, and the ratio of Th17 to Treg cell frequency was significantly increased along with increased SLEDAI scores. LN patients had a lower percentage and expression of FoxP3 in CD4+CD25^high T cells than SLE patients without nephritis. The concentration of TGF-β1 was found decreased in SLE patients compared with that from healthy controls, though no significant difference was found between LN patients and SLE patients without nephritis. The expression of IL-17 levels in LN patients exhibited a significant increase compared with patients without nephritis and healthy controls. Based on our results, the significantly elevated Th17 cells are accompanied by FoxP3+ Treg cells decrease in lupus nephritis, suggesting that Th17/Treg functional imbalance may be involved in the pathogenesis of renal damage in SLE patients.